1. Field of the Invention
The present invention relates to a method for recognizing a pattern of an alignment mark on a wafer. More particularly, the present invention relates to a method for recognizing a pattern of an alignment mark on a wafer in a measurement system during an initial set-up step.
2. Description of the Related Art
In the semiconductor industry, very large and expensive instruments are required from the initial manufacturing step of a semiconductor manufacturing line. Thus, it is important that the number of failures generated during a semiconductor manufacturing process should decrease in accordance with developments in the manufacturing technique in order to reduce the cost of the semiconductor manufacturing process. To reduce the number of failures in the semiconductor manufacturing process, measurement apparatuses are used to measure parameters relative to a wafer at a series of points in the semiconductor manufacturing line. In particular, the measurement of the parameters of the wafer becomes increasingly important as semiconductor devices become more highly integrated and have increasingly minute structures.
During the semiconductor manufacturing process, films are repeatedly deposited on a wafer and repeatedly etched. Frequently, a measurement apparatus is used to measure a thickness of the deposited film, an etched depth of the film, and a thickness of the remaining film. When the measurement apparatus measures such parameters relative to the wafer, the position and the amount of the film on the wafer are critical.
After the measurement apparatus measures the parameters of the wafer, a charge coupled device (CCD) camera, for example, is used to detect an image of an alignment mark. The detected image is then utilized as the reference data. During this process, a user should repeatedly reset the measurement apparatus for recognizing a pattern on the wafer or the measuring process may be skipped due to a measurement failure if a pattern recognition failure by the measurement apparatus occurs.
For example, it becomes significant that a measurement failure may occur at about 200 points in a semiconductor manufacturing line when the measurements of the wafer are performed at about 500 points of the semiconductor manufacturing line.
In operation, the measurement apparatus recognizes an alignment pattern in an initial setting step, and performs an alignment of the wafer with reference to the recognized alignment pattern. Thus, a measurement failure is generated when a pattern recognition failure occurs in the initial setting step.
In a conventional measurement apparatus, the alignment failure is typically generated when a particle on the wafer is mistaken for a pattern because the alignment set-up is performed to detect an image in a wide alignment region at a low magnification.